The Role of Surface Reactions in De-NOx Processes in Corona Discharge-Catalyst (or Zeolite) Hybrid Systems

The objective of this work was to explain the efficient NOx removal from simulated flue gas observed in the hybrid corona discharge-catalyst hybrid systems with either V2O5/TiO2catalyst or zeolite, both at room temperature. The simulated flue gas was a mixture of N2(80%):O2(5%):CO2(15%):NO (200 ppm). After analysing the results of several experiments on NOx removal in the corona discharge-catalyst (or zeolite) systems, two different mechanisms of NOx conversion in the hybrid systems are proposed. In the positive corona discharge-catalyst system, NOx molecules are removed due to the activation of the catalyst surface by the corona discharge (TiO2+ ε (≥ 3.2 eV) → hole++ e), which is followed by: (a) the catalyst surface driven formation of NH2radicals (which reduce NOx into N2in gas phase) and H+(or NH4 +) ions, (b) the oxidation of NOx to surface-trapped NO3-. The NO3-ions trapped on the catalyst surface are precursors of the formation of NH4NO3aerosols depositing on the catalyst surface. In the corona discharge-zeolite system, the conversion of NOx into NH4NO3, N2and H2O occurs due to the reactions involving zeolite-fixed NH4+ions.